java.util.Arrays $ ArrayList是什么意思？

Question

我不断收到以下错误消息

File: C:\Users\jiangbuyun\Desktop\p5\p5pack\P5Tests.java  [line: 1084]
Failure: java.lang.AssertionError: expected: java.util.Arrays$ArrayList<[A:X, B:X, C:X]> but was: java.util.ArrayList<[A:X, B:X, C:X]>

我有一堂课叫电路。这是一些领域。

private List<Contact> inputs, outputs;
private List<Wire> innerWires;

这就是我获取输入的方法

public void parseContactsLine(String line){
    Scanner sc = new Scanner(line);
    int i=0; //token's position
    while (! sc.hasNext("->")){
      Wire w = new Wire (sc.next());
      innerWires.add(w);
      Contact c = new Contact(innerWires.get(i),innerWires.get(i),true);
      inputs.add(c);
      i++;
    }

我的测试用例：

public void circuit_parseContactsLine1(){
    List<Contact> empty = Arrays.asList(new Contact[]{});
    assertEquals(empty, vanillaCircuit.getInputs());
    assertEquals(empty, vanillaCircuit.getOutputs());
    List<Contact> ins = Arrays.asList(new Contact[]{
      new Contact(new Wire("A"), new Wire("A"), true),
        new Contact(new Wire("B"), new Wire("B"), true),
        new Contact(new Wire("C"), new Wire("C"), true)}
    );
    List<Contact> outs = Arrays.asList(new Contact[]{
      new Contact(new Wire("D"), new Wire("D"), false)}
    );

    vanillaCircuit.parseContactsLine("A B C -> D");
    assertEquals(ins , vanillaCircuit.getInputs ());
    assertEquals(outs, vanillaCircuit.getOutputs());
  }

似乎此错误是由于ArrayList与List之间的比较引起的。测试用例使用Array.asList（）获得“输入”，而我的方法也返回一个arraylist。谁能向我解释java.util.Arrays $ ArrayList的意思？

我尝试输入时的错误。add（Arrays.asList（c））;

File: C:\Users\jiangbuyun\Desktop\p5\p5pack\Circuit.java  [line: 48]
Error: no suitable method found for add(java.util.List<Contact>)
    method java.util.Collection.add(Contact) is not applicable
      (argument mismatch; no instance(s) of type variable(s) T exist so that java.util.List<T> conforms to Contact)
    method java.util.List.add(Contact) is not applicable
      (argument mismatch; no instance(s) of type variable(s) T exist so that java.util.List<T> conforms to Contact)

Answer 1

java.util.Arrays$ArrayList是在Arrays实现List接口的类内的嵌套类。此实现具有固定长度，并由数组支持。

该方法Arrays.asList返回此类的实例。